1. Field of the Invention
The present invention relates to a semiconductor device in which an integrated circuit is formed by using a semiconductor layer. Particularly, the present invention relates to a manufacturing method of a semiconductor device including a sensor such as a photoelectric conversion element, and an active circuit.
2. Description of the Related Art
A number of photoelectric conversion elements using for detecting electromagnetic waves are generally known, and for example, a photoelectric conversion element having sensitivity to ultra-violet rays to infrared rays is referred to as a light sensor (also referred to as photosensor) in general. A light sensor having sensitivity to a visible light region with a wavelength of 400 nm to 700 nm is particularly referred to as a visible light sensor, and a large number of visible light sensors are used for devices which need illuminance adjustment, on/off control depending on human living environment, or the like.
In particular, in a display device, brightness in the periphery of the display device is detected so as to adjust display luminance thereof. It is because unnecessary electric-power can be reduced by detecting ambient brightness and obtaining appropriate display luminance. For example, such a light sensor for adjusting luminance is used for a mobile phone and a personal computer.
In addition, as well as ambient brightness, luminance of a backlight of a display device, particularly, a liquid crystal display device is also detected by a light sensor to adjust luminance of a display screen.
In such a light sensor, a photodiode is used for a sensing part and an output current of the photodiode is amplified in an amplifier circuit. As such an amplifier circuit, for example, a current mirror circuit is used (refer to Patent Document 1: PCT International Publication No. 04/068582).
According to Patent Document 1, a light sensor is manufactured over a first substrate, separated from it and then attached on a second substrate sequentially.
In addition, a technique is known in which an element is formed over a substrate with a release layer interposed therebetween and the substrate and the element is separated by laser irradiation (refer to Patent Document 2: Japanese Published Patent Application No. 2003-163337, and Patent Document 3: Japanese Published Patent Application No. 2004-221568).
According to Patent Documents 2 and 3, a metal layer such as tungsten (W) layer can be used as the release layer.